This invention relates to devices for reading, writing and storing bit-encoded data, and more particularly to disk drives including packs of multiple, concentrically stacked disks mounted to rotate on stationary spindle shafts.
The ongoing effort to increase data storage capabilities of magnetic disk drives and other data storage devices is concerned largely with increasing the density at which data can be stored on the available recording surface area. Another approach involves mounting multiple disks integrally, concentrically and axially spaced apart from one another as part of a single spindle assembly. Such assemblies typically include an elongate spindle shaft, a hub that directly supports the disks, and bearing assemblies at opposite ends of the spindle shaft to support the hub and disks for rotation relative to the disk drive housing. Further, an actuator is mounted movably relative to the housing for supporting several data transducing heads. The actuator (usually a rotary actuator) moves the transducing heads to selectively position them relative to the disks.
The spindle shaft can be mounted to rotate relative to the housing through bearings. Alternatively, the spindle shaft can be stationary or fixed within the housing, with the hub and disks mounted to rotate on the shaft. This latter approach allows a more secure, fixed mounting of the shaft to reduce vibration, mass and inertia of rotating parts. Thus, a stationary spindle shaft facilitates use of higher data storage densities, by enabling a more precise alignment of the disk pack and rotary actuator, and by enhancing stability during spindle rotation.
In the highly competitive disk drive market, however, further considerations must be addressed. The disk drive housing must be strong, light weight, resistant to vibration, and provide an effective seal to prevent contamination of the housing interior, particularly near the disks. Cost considerations stimulate efforts to employ less expensive materials and reduce the number of parts and steps involved in assembling the disk drive. Disk drives are frequently subject to size constraints. For example, the three and one-half inch magnetic disk drive is subject to an industry standard governing maximum dimensions for length, width and height of five and three-fourths, four, and one and five-eighths inches, respectively. A further consideration, particularly when different materials are interconnected or contiguous, is the need to minimize changes in component alignment due to differences in coefficients of thermal expansion.
Considerations of alignment, cost and maximum height play a role in determining how the spindle shaft and rotary actuator shaft can be mounted within the disk drive housing. Tapped flange mounting, for example, requires substantial axial length to install a tapped flange to receive the spindle. This reduces the height available to accommodate an additional disk or a motor with enhanced length, higher efficiency windings. Press fit shaft mounting is costly, and difficult to assemble or rework. Mounting shafts using V-blocks or similar clamps requires axial space. Finally, direct butt joint mounting does not offer the precise alignment required for certain applications.
The recording surfaces of 31/2 inch drives include as many as 3,000 tracks per inch, for a spacing of about 0.0003 inches between adjacent tracks. Accordingly, slight deviations from tolerances and thermal mismatch can have a major impact on track seeking and track following accuracy during temperature changes.
Therefore, it is an object of the present invention to provide a means for precisely and rigidly mounting a spindle shaft, rotary actuator shaft or both within a disk drive housing, without unduly strict tolerances for the shaft or its mounting components.
Another object is to provide a means for mounting an elongate spindle or rotary actuator shaft between two opposed walls of a disk drive housing, using minimal axial space or height.
Yet another object is to provide a disk drive with low cost yet reliable approach to positioning and orienting a spindle shaft and a rotary actuator shaft, with respect to a common datum and therefore with respect to one another.
Still another object is to provide a mounting means which is extremely rigid and able to withstand high shock and vibration without any detectable movement at shaft/housing interfaces.